Using the Derivative of F(x) Given Below, Determine the Intervals $$f ^ { \prime } ( x ) = ( x - 6 ) e ^ { - x }$$

Multiple Choice

Using the derivative of f(x) given below, determine the intervals on which f(x) is increasing or decreasing.
- $$f ^ { \prime } ( x ) = ( x - 6 ) e ^ { - x }$$

A) Decreasing on $( - \infty , - 6 )$ ; increasing on $( - 6 , \infty )$
B) Increasing on $( - \infty , - 6 )$ ; decreasing on $( - 6 , \infty )$
C) Increasing on $( - \infty , 6 )$ ; decreasing on $( 6 , \infty )$
D) Decreasing on $( - \infty , 6 )$ ; increasing on $( 6 , \infty )$